Eww, do you have any idea where that cash has been? Or how many people have touched it? Biologist Jane Carlton is leading the Dirty Money Project at New York University, in which researchers have identified about 3,000 types of bacteria on each dollar bill they study. Most are benign, but there is the potential for dangerous drug-resistance strains to spread from person to person by cash.

So far, Carlton and her colleagues have sequenced all the DNA found on about 80 dollar bills from a Manhattan bank. Their findings aren't published yet. But she gave Shots a sneak peak of what they've found so far.

The most common microbes on the bills, by far, are ones that cause acne. The runners-up were a bunch of skin bacteria that aren't pathogenic: They simply like to hang out on people's bodies. Some of these critters may even protect the skin from harmful microbes, Carlton says.

Other money dwellers included mouth microbes — because people lick their fingers when they count bills, Carlton says — and bacteria that thrive in the vagina. "People probably aren't washing their hands after the bathroom," she says.